Struts and elastic cords have long been utilized in tensile-integrity structures, or tensegrities as they are called, to provide the discontinuous compression and continuous tension members characteristic of such structures. Buckminster Fuller's U.S. Pat. No. 3,063,521 is an early explanation of such strut-cord units. Caps are illustrated on the slotted ends of the struts in that disclosure and another form of caps is shown in U.S. Pat. No. 4,148,520.
Some designs of strut-cord units are adapted particularly for model kits in which they can be assembled into tensegrities of various sizes and designs. A full discussion of one form of such strut-cord units for model kits is found in "Tensegrity: Introductory Theory and Model Construction" by Robert Gripp, copyrighted in 1978 and available from the Buckminster Fuller Institute in Philadelphia, Pa., U.S.A. The struts described in that publication are simple dowels with longitudinal slots cut into their respective ends and the associated cords are ordinary closed-loop rubber bands which extend with double runs between the slots. It is recognized that strut-cord units in model kits may be designed to construct various sizes of tensegrities and therefore U.S. Pat. No. 4,614,502 proposes that the struts be telescopic so that their lengths can be varied.
It is a primary purpose of the present invention to provide a strut-cord unit for tensegrities, especially for model kits, which allows for variations in construction by varying the stretch of the elastic cord while employing struts of a fixed length. It is a further object of the invention to avoid the double run aspect of closed-loop rubber bands by providing single-strand elastic cords. It is also an object of the invention to equip the struts with end caps which not only improve the appearance of the assembly but also serve to hold in place the cord portions passed through the slots in the ends of the struts.